Which of the compounds would you expect to have the highest melting point NaCl, H2Se, O2, H2O, H2S, CO2, MgO?

1 Answer
Mar 6, 2018

"MgO" has the highest melting point, by a large margin.

Explanation:

Ionic compounds have higher melting points than covalent compounds with small molecules. So the answer must be "NaCl" or "MgO".

Compare these compounds. Sodium chloride has +1 and -1 ion, magnesium oxide has +2 and -2. Also the charge centers are closer together for magnesium oxide because its oxide ion is much smaller than the chloride ion in sodium chloride. So the ions in "MgO" are more tightly bound, giving it a melting point of about 2800°C versus 801°C for "NaCl" and less still for the covalent compounds in the list.